Process for porcelain enameling and forming sheet metal



Nov. 26, 1968 J. T. GARTRELL 3,412,589

PROCESS FOR PORCELAIN ENAMELING AND FORMING SHEET METAL Filed July 1s, 196e United States Patent O1 ce 3,412,589 PROCESS FOR PORCELAIN ENAMELING AND FORMING SHEET METAL John T. Gartrell, Orwigsburg, Pa., assignor, by mesne assignments, to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware Filed July 18, 1966, Ser. No. 565,997 12 Claims. (Cl. 72-46) ABSTRACT OF THE DISCLOSURE The disclosure relates to a method of porcelain enameling and deforming sheet metal which includes applying porcelain enamel slip to the metal and firing the slip and then deforming the porcelain coated metal sheet at a temperature at which the porcelain enamel is plastic.

This invention relates to a process for enameling and forming sheet metal and more particularly to a process for deforming porcelain enameled sheet metal into the desired configuration.

A purpose of this invention is to provide an improved method for deforming porcelain enameled metal sheets.

A further purpose is to prevent distortion of the metal in the making of porcelain enameled deformed metal sheets.

A further purpose of this invention is to provide a process for deforming porcelain enameled metal which comprises applying a porcelain enamel slip to the metal, firing the metal and subsequently deforming the enameled metal into the desired shape.

A further purpose is to deform the porcelain enameled metal while it is at a temperature within the range of the plasticizing temperature of the porcelain.

A further purpose is to pass a porcelain enameled sheet of metal previously fused between deforming rollers that have been heated to a temperature sufiicient to maintain the temperature of the metal sheet during deforming within the plasticizing range of temperatures of the porcelain enamel.

A further purpose is to deform porcelain enameled metal without cracking the porcelain or without allowing it to run or otherwise form a discontinuous coating on the metal sheet.

A further purpose is to eliminate any necessity for annealing the metal after deforming to re-fuse any cracked porcelain by maintaining plasticizing temperatures during the deforming of the metal sheet.

A further purpose is to provide an improved continuous process for deforming porcelain enameled metal sheets.

A further purpose is to provide a low cost production of vitreous porcelain enamel coated formed metal sheets having color continuity, high impact resistance, Wearability and standardization to meet existing construction material standards.

Other purposes and advantages will become apparent from the following description and drawing illustrating embodiments of the method of this invention wherein:

FIGURE l is a diagrammatic View illustrating a method for carrying out the objects of this invention on a continuous basis.

FIGURE 2 is a sectional View taken along the lines 2 2 of FIGURE 1.

FIGURE 3 is a diagrammatic view illustrating part of an alternative method for carrying out the invention, the ptortion beyond the firing ovens only being shown.

FIGURE 4 is a right side view of the alternative method illustrated in FIGURE 3 showing the final step in the process.

3,412,589 Patented Nov. 26, 1968 The porcelain enameling of metal is the application and firing of vitreous frits to metal sheets in order to form a glass-like surface on the metal that not only is resistant to chemicals, heat and fire but generally lends an attractive and colored appearance to the metal. Among a variety of uses, such glass enameled sheets have been used for architectural and structural panels and the like.

In the fusing of porcelain enamel to metal, it is conventional to apply a porcelain enamel slip and then to re individual sheets of the metal previously cut to the desired shape. More recently continuous processes for applying porcelain enamel to sheet metal have been developed wherein the sheet metal is fed through a succession of treating zones. First an enamel slip is applied to the metal suitably by spraying on either one or both sides of the sheet and then it is continuously passed through a heating or firing chamber Where the enamel is fused and bonded to the metal. Such continuous processes are shown for example in patents to Robert G. Calton, wherein the sheet is either held under tension as shown in U.S. Patent No. 2,428,307 or is suspended through the treating zones as shown in U.S. Pa-tent No. 2,580,406.

However, it is often desirable to impart various shapes to the porcelain enameled metal for use as wall panels or the ilke. A conventional panel might, for example, be corrugated and it has been the practice in the .past to first deform or corrugate the metal Iand then to Iapply the porcelain enamel slip to the deformed metal, as shown `for example in another patent fto Calton, U.S. Patent No. 2,480,711, in order to produce a corrugated enameled metal sheet. In such a process, the meal is cold rolled before enameling which places a strain in the sheet which may later cause distortion when such strain is relieved in varying amounts by the heat necessary to fuse and bond the enamel to the metal. In tan effort to eliminate this `distortion caused by cold rolling, heavier gauge metals, often heavier than are required, have to be used.

Therefore, and according to the objects of this invention, applicant has pnovided a process wherein the metal is deformed `subsequent to the application of the porcelain enamel in order to eliminate the cause of distortion in the metal. Furtherfore, the metal is deformed at a temperature Within the range of the plasticizing temperatures of the porcelain enamel so as to prevent cracking of the enamel on deformation `and also to prevent the enamel from running and forming a discontinuous coating if it was in the liquid state.

The plasticizing temperature of the porcelain enamel is defined as that temperature at which the porcelain is soft and plastic-like as opposed -to being a liquid so that it can be altered to conform with various configurations imparted to the metal to which it adheres without cracking or otherwise breaking up. It has `'been found that the plasticizing temperature of most porcelain enamels is approximately 200 to 300 F. below the fusion tempera- -ture of a porcelain enamel which is defined as a temperature at which the procelain will fuse into a continuous enamel finish and bond itself to the metal.

The procelain enamel is liquid at fusion temperatures land therefore while it is desirable to prevent cracking, it is also necessary to prevent the enamel from running or othewise becoming discontinuous `during deforming. Hence, by deforming the metal at the plasticizing temperature of the porcelain and subsequent to po-rcelainizing, the metal is prevented from being distorted and the porcelain surfaces are prevented from running and from cracking. This falso eliminates any need for reheating after deforming which would otherwise be necessary to re-fuse the enamel that cracked during deforming.

By way of an example only without limitation and with reference to FIGURE 1, there is shown a diagrammatic view illustrating a continuous method for carrying out the objects of this invention. There is shown a coil of sheet metal which is unwound and caused to be passed through a hot cleaning bat-h 11 containing solvents for removal of grease and other foreign matter. This hot bath may alternatively consist of a solution of nickel sulphate or similar composition as required to clean, etch, or deposit nickel on the steel. This may be used as a supplement to mechanical or solvent cleaning. Subsequent to the bath, the sheet is passed through a dryer 12 to remove the solvent and/ or residual moisture of any solution from the surface of the metal. The sheet is suitably motivated by a plurality of synchronized pinch rollers 13 suitably Idriven by a means not shown which pull the sheet through the various treating phases at a predetermined speed.

The metal sheet is first suspended in a continuous manner through a base-coat sprayer 14 which sprays a base coat of liquid vitreous porcelain enamel slip onto both sides of the metal. The spraying may be accomplished by one or more of a series of aspirators 15 located so as to uniformly spray the enamel slip onto the sheet. Alternatively, the sheet may be immersed in a bath of slip or through any other suitable application means compatible with a continuous process.

Subsequently, the sheet passes thnough a first firing oven 16 where the metal sheet and porcelain slip is heated to the fusion temperature of the porcelain to melt the porcelain fusing it into a continuous coating and bonding it to the surface of Athe metal. The oven may be either electrically heated or be heated by the products of combustion or other suitable means. It should be eiciently designed with good insulation and a Iminimum opening size for entrance and exi-t of the metal so that the porcelain will heat and fuse in the least amount of time so as to increase the eiciency of the process.

The metal then passes through `another set of drive rollers 13 and into a color sprayer or finish coat sprayer 17 similar to the base-coat sprayer 14 where the desired color coat of liquid vitreous porcelain enamel slip is applied, `suitably by spraying to one side as shown or to both sides of the metal. Subsequent to the :application of the finish slip, the sheet passes through a second furnace or firing over 18 wherein the finish porcelain enamel coat is heated to fusion temperature to fuse porcelain enamel and bond it tothe first coat.

While a more durable coating of enamel is achieved by first applying a base coat to the metal and t-hen a finish coat, it is to be understood that the invention is equally applicable to processes wherein all the porcelain enamel is applied to the metal in one application.

The process up to this point is conventional and well known to those skilled in the art as a method for porcelainizing a fiat metal sheet on a continuous basis. However, the process of this invention is directed to the method of deforming these porcelainized fiat strips of metal without damaging the metal or the procelain coating by su-bsequently passing Vthe sheet through a drive unit and into a forming device 19 that shapes the sheet metal into the desired configuration,

In the deforming of metal, it is necessary to the process of this invention, as described above, that the porcelain enamel sheet be kept within the range of the plasticizing temperatures of the enamel. In order to maintain this temperature, the forming elements or rollers 20 of the deforming device 19 are heated to a certain temperature which is below the melting temperature of the enamel. Since the enameled sheet will have been heated to the fusion temperature of the enamel in the firing over 18, the heated rolls do not heat the sheet to the proper temperature but merely reduce or prevent a loss of heat from the metal sheet so that the plasticizing range of temperatures as defined above can be maintained during forming.

The forming elements may be disposed longitudinally with respect to the direction of motion of the sheet as is well known in the art suitably forming ribs, channels,

flanges or corrugations as shown for example in FIG- URE 2.

It is to be understood that any shape can be imparted to the porcelainized metal by deforming rollers without departing from the scope of this invention. After emerging from the forming device, the sheet passes through a flying shear or other suitable cutting means 21 that permits the sheet to be cut into specified lengths and stacked as shown in the drawing.

By way of a specific example, when it is desired to porcelainize and deform thin metal steel sheets, where the fusion temperature of a commercial steel enamel is around 14S0 F., the softening or plasticizing range of temperatures of the slip has been found to be approximately 200 to 300C7 F. less than the fusion temperature or within a range of from 1150 to l250 F. Thus in order to prevent a major loss of heat from the sheet during deforming by convection, conduction or radiation and to keep the temperature within this last mentioned range of temperatures, it is necessary to heat the forming rollers to a temperature just below the plasticizing temperature of the porcelain enamel. By establishing this temperature differential the proper temperature of the enamel sheet can be maintained during deforming.

Since the fusion temperatures of various metal enamels are well known in the art, the proper temperatures to be maintained and the proper temperature in the rolls can easily be derived therefrom as described above. While the plasticizing range of temperature varies between enamel compositions and the metals to which they are bonded, it has been discovered that the plasticizing temperature is generally 200 to 300 F. below the fusion temperature of the particular porcelain enamel composition.

Alternatively, the process may be made discontinuous without departing from the scope of this invention. Hence, if it is desired, the metal may be cut into the desired length or shape after enameling and before it is deformed. When it is desired to form these sheets, the heat in them must be retained or they must otherwise be reheated so that temperature of the sheet is within the plasticizing range of the enamel during deforming of these sheets. By maintaing this temperature during deforming, the vitreous porcelain enamel metal is kept at a temperature that insures that the coating is in a semiliquid or plastic state permitting it to follow the metal as it is being formed without cracking or without running if it was too hot and therefore too liquid.

Such an alternative process is shown diagrammatically in FIGURES 3 and 4 wherein the metal is out into the desired lengths immediately upon emerging from the drive unit 13 after the last firing oven 18 :by a flying shear 25. This cuts the continuous strip of enameled metal into individual sheets, the forward end of a sheet passing into another oven 26 that maintains the temperature in the sheet until the rear end of the sheet has emerged from the firing oven and has been sheared off at the desired length. Suitably this oven 26 is maintained at or near the range of plasticizing temperatures of the enamel as described above.

The individual sheets are then caused to travel at right angles or crosswise to the longitudinal direction of the continuous metal strip through a deforming machine 27 wherein the deforming elements in the form of rollers 28 are disposed transverse to the direction of motion of the sheets. The rollers 28 are heated to a temperature below the melting temperature of the enamel in order to maintain the temperature of the porcelain enamel sheet within the range of the plasticizing temperature of the enamel similar to the continuous method described above.

By severing the enamel metal strip into specific lengths the deforming operation is not dependent upon the speed of the enameling process and therefore can be accomplished with greater speed and with a minimum of heat loss. As shown in FIGURE 4 this process produces longitudinally corrugated enameled sheets identical to those formed in the continuous process described above.

Instead of heating the forming elements, themselves, hot air or other suitable heating atmospheres may be supplied to the forming device in a conventional manner in order to supply the necessary heat to establish the proper temperature differential to keep the enamel at the softening or plasicizing temperature.

By enameling and forming according to the process of this invention, a formed metal sheet is obtained having a uniform coating of porcelain thereon similar to that only heretofore obtainable on flat pieces of metal. The process furthermore alleviates the problem of distortion in formed metal sheets and permits a low cost continuous production of deformed vitreous porcelain enameled coated metal sheets having color and enamel continuity that can be readily cut to fit standard material sizes.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the method shown, and I therefore claim all such insofar as they fall within the reasonable spirit and scope of my invention.

Having thus decsribed my invention what I claim as new and desire to secure by Letters Patent is:

1. A method for porcelain enameling and deforming sheet metal, which comprises feeding a fiat sheet of metal through a series of treating steps that includes, first applying a porcelain enamel slip to the metal, firing the slip at its fusion temperature and subsequently deforming the porcelainized metal sheet at a temperature within the range of the plasticizing temperature of the porcelain and thence cooling the sheet.

2. A method of claim 1, wherein the plasticizing temperature is maintained approximately 200-300 F. below the fusion temperature of the porcelain.

3. A method of claim 1, wherein the plasticizing temperature during deforming is maintained by heating deforming means to a temperature sufficient to establish a temperature differential between the means and the fused sheet to maintain the porcelainized enameled sheet at its plasticizing temperature during deforming.

4. A method of claim 3, wherein the plasticizing temperature is maintained approximately 200-300 F. below the fusion temperature of the procelain by maintaining the deforming means at a temperature just below the plasticizing temperature of the porcelain.

5. A method according to claim 1, for continuously porcelain enameling and deforming sheet metal, in which the metal is deformed by passing the porcelainized metal between deforming rollers disposed longitudinally with respect to the direction of motion of the sheet metal.

6. A method according to claim 1, wherein the porcelainized metal sheet is cut into specific lengths subsequent to firing and are then passed at right angles to its length through deforming rollers disposed transverse to the direction or motion of the individual lengths of the porcelainized metal sheet.

7. A method of claim 1, which includes initially apply- CFI ing a base coat of liquid vitreous porcelain enamcl slip. heating the enamel to its firing temperature, subsequently applying a finishing coat of liquid vitreous porcelain enamel slip and then reheating to the fusion temperature of the enamel to fuse the finish coat and bond it to the base coat prior to deforming the metal sheet.

8. A method for continuously porcelain enameling and deforming a metal sheet, which comprises continuously feeding a fiat strip of metal through a plurality of treating zones that includes spraying a porcelain enamel slip onto the metal, firing the strip by heating it to its fusion temperature, immediately passing the heated sheet through a roll corrugator wherein the rolls are heated to a temperature below the fusion temperature of the porcelain that is sufficient to keep the temperature of the enameled sheet within the range of its plasticizing temperature during deforming and thereafter cooling the sheet and cutting it into desired lengths.

9. A method of claim 8, wherein the plasticizing temperature is maintained approximately 200-300 F. below the fusion temperature of the porcelain by heating the roll corrugator to a temperature just below the plasticizing temperature of the porcelain.

10. A method for porcelain enameling and deforming a metal sheet, which comprises feeding a fiat strip of metal through a plurality of treating zones that includes spraying a porcelain enamel slip onto the metal, firing the strip by heating it to its fusion temperature, cutting the porcetairuzed metal into the desired lengths, immediately passing the heated sheet at right angles to its length through a roll corrugator wherein the rolls are heated to a temperature below the fusion temperature of the porcelain that is sufiicient to keep the temperature of the enameled sheet within the range of its plasticizing temperature during deforming and thereafter cooling the sheet.

11. A method of claim 10, wherein the plasticizing temperature is maintained 200-300 F. below the fusion temperature of the porcelain by heating the roll corrugator to a temperature just below the plasticizing temperature of the porcelain.

12. A method of claim 10, including passing the metal strip after firing into an oven to maintain the temperature of the sheet near the plasticizing temperature of the porcelain enamel until the strip is cut into the desired lengths and then immediately passing the heated sheet through the roll corrugator.

References Cited UNITED STATES PATENTS 2,480,711 8/1949 Calton 29-527 2,850,999 9/1958 Kaplan et al. 29-528 2,851,000 9/1958 Kaplan et al 29-527 2,851,372 9/1958 Kaplan et al 29-528 3,087,240 4/1963 Gross 29-528 3,154,426 10/1964 Kohnken 29-528 3,169,310 2/1965 Gibson et al 29-527 3,206,848 9/1965 Rentmeester 29-528 CHARLES W. LANHAM, Primary Examiner. E. M. COMBS, Assistant Examiner. 

